EP3913377A1 - Method and device for moving a trajectory in the vicinity of an object surface - Google Patents

Abstract

The invention relates to a method for flow measurement of fluids in the vicinity of an object surface (O) with a laser Doppler velocimeter (2) attached to parallel or serial kinematics with at least 6 degrees of freedom (1), the bisector (W) of the at least one Laser beam pair (I ₁, I ₂) of the laser Doppler velocimeter (2) always essentially orthogonal to the tangential planes T _i of Points P _i is positioned, as well as a method for determining a trajectory (B) in the vicinity of an object surface (O) with a device according to the invention, preferably from the coordinates x _i obtained , y _i, z _i of points P _i on an object surface (O) the coordinates x _i ', y _i ', z _i' of points P _i 'at a distance (a _i) to the object surface ( O), whereby between points P _i 'interpolie rt. The invention further relates to a device for following at least one trajectory (B) in the vicinity of the object surface (O), comprising parallel or serial kinematics with at least 6 degrees of freedom (1) and a device from the group of measuring devices or tools (2), characterized by a control or regulating device which contains geometry data of the object surface (O), the orientation of the device from the group of measuring devices or tools (2) along the trajectory (B) being defined from the geometry data, with the orientation is preferably orthogonal to the tangential plane T _i of a point P _i located on the object surface (O).

Description

The present invention relates to a method for measuring the flow of fluids in the vicinity of an object surface with a laser Doppler velocimeter attached to parallel or serial kinematics with at least 6 degrees of freedom. The invention also relates to a device for following a trajectory in the vicinity of the object surface, comprising parallel or serial kinematics with at least 6 degrees of freedom and a device from the group of measuring devices or tools, as well as a method for determining a trajectory in the vicinity of an object surface a device according to the invention.

BACKGROUND OF THE INVENTION AND PRIOR ART

Fluid mechanics plays an important role in many areas of technology. Mostly the optimization of the flow resistance of an object in fluids such as air or water or heat and mass transfer is in the foreground. Particularly in automobile and aircraft construction, particular attention is paid to aerodynamics, a sub-area of fluid mechanics, in order to optimize the driving and flight characteristics and thereby minimize the energy required to operate a vehicle or aircraft.

In addition to numerous mechanical methods for measuring fluid flows, with which the fluid flow is generally significantly influenced by the measurement itself, non-contact methods have been developed with which the change in the fluid flow due to the measurement is negligible.

In addition to particle image velocimetry (PIV), magnetic resonance velocimetry (MRV), particle tracking velocimetry (PTV), etc., laser Doppler anemometry (LDA) or laser Doppler Velocimetry applied.

Laser Doppler Velocimetry is an optical measurement method for the selective determination of velocity components in fluid flows. This also enables the point-by-point determination of oscillation states of object surfaces. Basically, laser Doppler velocimetry can be explained using two models, the Doppler model and the interference fringe model.

Doppler model:

In the context of the Doppler model, a difference frequency Δ f = f _R - f _{d is} determined, where f _R denotes the frequency of a reference wave and f _d denotes the frequency of the light scattered by a moving particle. The frequency f _{d of} the scattered light is Doppler shifted to the frequency f _{l of} the laser light.

für die Geschwindigkeitskomponente in Richtung der Laserstrahlachse e _l , entsprechend dem Produkt der halben Wellenlänge λ_l des eingestrahlten Lasers und der gemessenen Differenzfrequenz Δf. When using a single-beam laser Doppler system, for example, the oscillation state of object surfaces can be determined by directing the laser beam onto a specific point on the object surface. If the scattered light is superimposed in backscattering (scattering angle 180 °) with a reference wave of frequency f _R = f _l, this results $$v_{{\overrightarrow{\mathrm{e}}}_l}=\frac{{\mathrm{<figure-callout\; id="2"\; label="\lambda \; l"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_l}{2}\cdot \mathrm{\Delta }\mathit{f}$$

for the speed component in the direction of the laser beam axis e _l , corresponding to the product of half the wavelength λ _{l of} the incident laser and the measured difference frequency Δ f.

für die Geschwindigkeitskomponente orthogonal zur Winkelhalbierenden der beiden Laserstrahlen. Man spricht bei einer solchen Anordnung der Laser von einem Laser-Doppler-Velocimeter (LDV).A two-beam laser Doppler system is preferably used to measure the speed of flows. There are two (coherent) laser beams with axis orientations e _{l 1} and e _{l 2} brought to the intersection at an angle of 2 ϕ, the particles of a flow illuminated at the intersection or intersection point, the light of the two laser beams with different Doppler shifts, corresponding to the frequencies f _{d 1} and f _{d 2} , sprinkle. When the two scattered waves are superimposed on a detector to measure the difference frequency Δ f, the result is $$v_{{\overrightarrow{\mathrm{e}}}_{\perp }}=\frac{{\mathrm{<figure-callout\; id="2"\; label="\lambda \; l"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_l}{2\mathit{sin\phi }}\cdot \mathrm{\Delta }\mathit{f}$$

for the velocity component orthogonal to the bisector of the two laser beams. Such an arrangement of the lasers is called a laser Doppler velocimeter (LDV).

Interference fringe model:

(idealerweise äquidistant) beabstandet und parallel zur Winkelhalbierenden der beiden sich schneidenden Laserstrahlen ausgerichtet sind. Ein durch das Interferenzmuster bewegtes Partikel streut das Licht der Interferenzstreifen periodisch mit einer messbaren Signal-Frequenz f_S . Somit errechnet sich die Geschwindigkeitskomponente eines Partikels orthogonal zu den Interferenzstreifen aus $$v_{{\overrightarrow{e}}_{\perp }}=\frac{{\lambda }_l}{2\mathit{sin\phi }}\cdot f_s$$

in Übereinstimmung mit dem Dopplermodell unter Verwendung eines Zweistrahl-Laser-Doppler-Systems für f_S = Δf. In the interference fringe model, which applies to particle sizes d ≪ λ _l , the interference of the two laser beams at the point of intersection or intersection (measurement volume) is considered. For coherent laser beams, a static interference pattern is created, with the (essentially straight) interference fringes by a distance $$\mathrm{\Delta }\mathit{x}=\frac{{\mathrm{<figure-callout\; id="2"\; label="\lambda \; l"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_l}{2\mathit{sin\phi }}$$

(ideally equidistant) and aligned parallel to the bisector of the two intersecting laser beams. A particle moving through the interference pattern scatters the light from the interference fringes periodically with a measurable signal frequency f _S. The velocity component of a particle is thus calculated orthogonally to the interference fringes $$v_{{\overrightarrow{e}}_{\perp }}=\frac{{\mathrm{<figure-callout\; id="2"\; label="\lambda \; l"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_l}{2\mathit{sin\phi }}\cdot f_s$$

in accordance with the Doppler model using a two-beam laser Doppler system for f _S = Δ f.

The combination of several laser pairs of different wavelengths enables the measurement of speed components in several directions, the laser pairs generally having a common intersection point and thus a common measurement volume. The interference patterns of the different laser pairs are at a defined angle to one another.

To measure flow velocities in the area of objects such as turbines, wings, spoilers, pipes, etc., LDVs, in particular two-beam laser Doppler systems (two-beam LDV) or multi-beam LDVs, are typically used on rigid traversing systems with one to three translational Degrees of freedom and an axial rotational degree of freedom attached. Thus, the positioning and orientation of the measuring volume of a two-beam LDV is possible in a maximum of four degrees of freedom.

The publication NC Temperley et al. / Flow Measurement and Instrumentation 15 (2004) 155-165 discloses the assembly of a multi-jet LDV on a 6-axis robot, with which the flow velocity of water in a flow meter is determined. The measurement takes place from two directions, the bisector of the both laser pairs are aligned either parallel to the x -axis or parallel to the y -axis. The measuring volume is positioned in measuring points in previously defined planes, the planes being marked with black rubber rings. Each measuring point in the plane is approached from one direction ( e.g. from + y to - y and from - z to + z ).

All methods known from the prior art for measuring the flow of fluids in the area of an object surface, in particular in the vicinity of an object surface, have the disadvantage that the measurement takes place in previously defined measuring points, with a spatial displacement of the object surface or a movement of the object surface is not taken into account. This disadvantage generally exists when the exact positioning of a measuring device or a tool in the vicinity of an object surface is required.

Another disadvantage is that in order to measure more than one velocity component of a flow in a plane by means of a two-beam LDV, more than one measurement must be carried out at one point.

The object of the present invention is therefore to provide a device and a method in order to eliminate the disadvantages mentioned. For example, a measurement or production plan for any definition of measurement or production points - or their position and orientation - can be relative to the (measurement) object (e.g. tangentially along an object surface). These can be transferred to kinematics to carry out the measurement or production.

BRIEF DESCRIPTION OF THE INVENTION

An essential aspect of the underlying task is achieved by a method for measuring the flow of fluids in the vicinity of an object surface with a laser Doppler velocimeter (LDV) attached to parallel or serial kinematics with at least 6 degrees of freedom, the LDV at least one intersecting laser beam. Pair, the common point of intersection of the at least one laser beam pair forming a measurement volume, the measurement volume having at least one interference pattern with interference fringes, the interference fringes being aligned parallel to the bisector of the at least one laser beam pair, the successive points P _i ' ( i = 1, ..., N ), the speed of a fluid flow being measured at the points P _i ' , the points P _i ' each at a certain distance a _i lie on a line L _i to the object surface, the lines L _i each being orthogonal to the tangential planes T _{i of} the points P _i on the object surface (O) (with P _i ≠ P _{i + j} , j ∈ {1 ,. .., N }) and the points P _i lie on the lines L _i , the bisector of the at least one laser beam pair always being essentially orthogonal to the tangential planes T _{i of} the points P _i for i = 1, ..., N is positioned.

oder $\left|{\overrightarrow{v}}_i\right|=\sqrt{v_{x_i}^2+v_{z_i}^2}$

oder $\left|{\overrightarrow{v}}_i\right|=\sqrt{v_{y_i}^2+v_{z_i}^2}$

gegeben ist, wobei v_xi , v_yi und v_zi die Geschwindigkeitskomponenten der Fluidströmung in die drei Raumrichtungen bezeichnen.It is preferably provided that in the points P _i ' ( i = 1, ..., N ) the amount of the resulting speed v _i a fluid flow is measured, the resulting speed depending on the orientation of the measurement volume through $\left|{\overrightarrow{v}}_i\right|=\sqrt{{\mathrm{<figure-callout\; id="2"\; label="v\; x\; i"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">v</figure-callout>}}_{x_i}^{{}_{}}+{\mathrm{<figure-callout\; id="2"\; label="v\; y\; i"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">v</figure-callout>}}_{y_i}^{{}_{}}}$

or $\left|{\overrightarrow{v}}_i\right|=\sqrt{v_{x_i}^2+{\mathrm{<figure-callout\; id="2"\; label="v\; z\; i"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">v</figure-callout>}}_{z_i}^{{}_{}}}$

or $\left|{\overrightarrow{v}}_i\right|=\sqrt{{\mathrm{<figure-callout\; id="2"\; label="v\; y\; i"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">v</figure-callout>}}_{y_i}^{{}_{}}+{\mathrm{<figure-callout\; id="2"\; label="v\; z\; i"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">v</figure-callout>}}_{z_i}^{{}_{}}}$

is given, where v _{x i} , v _{y i} and v _{z i} denote the velocity components of the fluid flow in the three spatial directions.

For the measurement in the points P _i 'it can be provided that the coordinates x _i , y _i , z _i of points P _i on the object surface are first extracted directly from an existing geometry model, such as a CAD model or can be determined by a method for detecting 3D object surfaces. On the basis of the knowledge obtained therefrom about the geometry of the object surface, the coordinates x _i ', y _i ', z _i 'of points P _i ' at a distance a _{i from} the object surface can be determined.

In one embodiment it is provided that the determination of the coordinates x _i , y _i , z _{i of} all points P _i on the object surface takes place immediately before the flow measurement.

"Immediately before the flow measurement" means that the time between the determination of the coordinates of all points P _i and the flow measurement or the speed measurement of a flow in these points is due to the time required for the data processing and for the forwarding of the data (coordinate information ) is limited to the parallel or serial kinematics.

It is particularly preferably provided that the determination of the coordinates x _i , y _i , z _{i of} all points P _i and / or the registration of a change in the coordinates x _i , y _i , z _{i of} all points P _i in real time, ie essentially during of the (speed) measurement process, takes place. What these method variants have in common is that the coordinates x _i ', y _i ', z _i 'of points P _i ' at a distance a _{i from} the object surface, in particular immediately following, are determined from the obtained coordinates x _i , y _i , z _i .

The measurement of the velocity of a fluid flow is carried out essentially exactly once at each point P _i ′ , as a result of which a vector field F describing the fluid flow is generated.

In order to guarantee the exact positioning of the measurement volume at a point P _i ' , it is provided that the Tool Center Point (TCP) of the LDV is determined by means of a calibration unit, the TCP of the LDV being the translational and rotational displacement relative to the center point of the tool holder indicates parallel or serial kinematics with at least 6 degrees of freedom.

The object set at the beginning is also achieved by a device for following a trajectory in the vicinity of the object surface, comprising parallel or serial kinematics with at least 6 degrees of freedom, in particular a 6-axis industrial robot, and a device from the group of measuring devices or tools with a tool coordinate system , characterized by at least one control or regulating device which contains geometry data of the object surface, the orientation of the device from the group of measuring devices or tools along the trajectory being defined from the geometry data, the tool axis being orthogonal to the tangential plane T. _{i of} all points P _i ( i = 1, ..., N ) located on the object surface.

In one embodiment, the control or regulating device is divided into a central control or regulating device and a control or regulating unit of the parallel or serial kinematics with at least 6 degrees of freedom. The central control or regulating device is connected to the control or regulating unit of the parallel or serial kinematics with at least 6 degrees of freedom via a data line, the control or regulating unit controlling the alignment of the device from the group of measuring devices or tools along the trajectory . Any physical transmission medium commonly used in information and communication technology can be used for the data lines. Transmitter-receiver transmission channels based on radio or electromagnetic waves also fall under the term data line in this context.

The alignment of the device from the group of measuring devices or tools is made possible by defining a tool coordinate system whose origin is the TCP. The tool axis, on the basis of which the orientation of the device from the group of measuring devices or tools is defined, corresponds to the z-axis of the tool coordinate system. The control or regulating device can thus control the orientation of the device according to the tool axis via the serial or parallel kinematics with at least 6 degrees of freedom.

In a further embodiment variant, it is provided that the control or regulating device receives data from a device for the contact-free detection of 3D object surfaces, a geometry model being generated from the data obtained.

It is particularly preferred that the control or regulating device has a postprocessor, the postprocessor translating the instructions for the parallel or serial kinematics with at least 6 degrees of freedom, the control or regulating device controlling and / or regulating the actuators of the parallel or serial kinematics and specifies and / or monitors the movement along the at least one trajectory.

In one embodiment variant, a data processing device, for example a computer with CAD / CAM software, generates a geometry model, in particular a CAD model. A flow chart in the form of a program can be created from this model using CAM software or software such as MATLAB, for example. A postprocessor translates this flow chart into a further program (or the existing program into another programming language), which the control or regulation unit of the parallel or serial kinematics can process with at least 6 degrees of freedom.

The device from the group of measuring devices or tools is preferably an LDV. The LDV is particularly preferably designed as a two-beam laser Doppler system. In a variant, it can also be designed as a multi-beam laser Doppler system. To determine the TCP of the LDV, it can be provided that a device according to the invention has a calibration unit for the LDV, the calibration unit having an image sensor.

The TCP of the LDV indicates the translational and rotational displacement relative to the center point of the tool holder of the parallel or serial kinematics with at least 6 degrees of freedom. In one embodiment variant, a laser cutting device, a welding device, a glue gun, a paint gun and the like are provided for the device from the group of measuring devices or tools.

It is preferably provided that the device for capturing a 3D object surface is a 3D scanning unit, in particular a 3D laser scanning unit. Alternatively, to capture the 3D object surface at least one camera, in particular at least one digital camera for photogrammetry, can be provided.

Another aspect of the underlying object is achieved by a method for determining a trajectory in the vicinity of an object surface using a device according to the invention, the object surface being detected with a device for contactless detection of a 3D object surface, whereby a three-dimensional point cloud corresponding to the object surface is obtained, characterized in that the points P _i on an object surface are assigned to a coordinate system and each point P _{i is assigned} coordinates x _i , y _i , z _i .

The coordinates x _i ', y _i ', z _i 'of points P _i ' at a distance a _{i from} the object surface are preferably determined from the obtained coordinates x _i , y _i , z _i of points P _i on an object surface, with between Points P _i 'is interpolated.

In one embodiment variant, it is provided that the device for detecting a 3D object surface is used to detect a movement of the object surface essentially in real time.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1

shows a device according to the invention for following a trajectory B in the vicinity of the object surface O.

Fig. 2

shows schematically two intersecting laser beams l ₁ , l ₂ . The crossing point or intersection point S forms a measurement volume M.

Fig. 3

shows an object with an object surface O. For illustration, three measuring points Pi '(with i = 1, 2, 3) along a trajectory B are shown.

DETAILED DESCRIPTION OF THE INVENTION

In Fig. 1 a device according to the invention for following a trajectory B in the vicinity of the object surface O and for detecting an object surface O is shown. The embodiment variant of a device according to the invention shown as an example has serial kinematics 1 with six degrees of freedom, an LDV 2, a device for contactless detection of 3D object surfaces 3 and a calibration unit 4.

The parallel or serial kinematics is preferably a 6-axis industrial robot, for example of the "ABB IRB 1200-7 / 0.7" type, although a device according to the invention is of course not to be restricted to this special industrial robot. A tool or a measuring device can be positioned at any location within the working area of the industrial robot, and the control or regulating unit of the industrial robot controls or regulates the actuators (motors of the individual actuators). As a result, a desired position and orientation of a tool or measuring device relative to the (measuring) object can always be achieved. The range of such an industrial robot is around 0.7 m with a positioning accuracy of 20 µm, but the use of industrial robots with ranges of several meters, for example up to 3.5 m, is conceivable.

In the text, the terms "parallel or serial kinematics with 6 degrees of freedom", "6-axis industrial robot" and "industrial robot" are used synonymously for the sake of readability. The terms "3D object surface" and "object surface" are also used synonymously.

A measuring device 2 can be an LDV of the "ILA Fp50 shift" type , wherein a device according to the invention can have any types of LDVs and any type of measuring device or tool. The type of LDV mentioned is a two-beam LDV, the two lasers l ₁ , l ₂ emitting light with a wavelength of 532 nm at a power of 100 mW. With such an LDV, particle or flow velocities of 0.01 to 150 m / s can be measured with a relative error of 0.3%.

A measuring device 2 such as an LDV or a tool is attached to the link furthest from the base of the serial kinematics. Common devices and fasteners for industrial robot tool flanges can be used as tool holders. Using the example of an LDV, a profile rail made of aluminum, for example, can be attached to the tool flange of the industrial robot. This profile rail can be extruded and have grooves. An LDV can be attached to such a profile rail, the position of the LDV being adjustable along the profile rail.

In an embodiment variant which has a device for contactless detection of 3D object surfaces 3, this can be, for example, a 3D scanning device or a plurality of 3D scanning devices, in particular a 3D laser scanning device. It is also conceivable that the device for the contact-free detection of 3D object surfaces consists of at least one camera. For example, the 3D object surfaces can be analyzed photogrammetrically.

Such a device for contactless detection of object surfaces 3 is connected via a data line to a data processing device (not shown), for example a computer. The computer calls up data from the device for contact-free acquisition of object surfaces 3, processes the acquired data with a software known for this purpose, whereby a 3D geometry model or a 3D CAD model is created and forwards the data to the control - or control unit of the 6-axis industrial robot.

Depending on the design variant, either a geometry model is created beforehand as described above or the control and regulation device of the parallel or serial kinematics already contains a geometry model in advance. From the geometry model, with known software or with known techniques, for example with CAM software (computer-aided manufacturing software) or commercial software such as MATLAB, a kind of flow chart can be created, with which it is determined along which Path curve or the path curves along which a tool or measuring device is navigated along the 3D object surface (offline programming). The sequence plan determined is then translated by a postprocessor into a program that can be processed by the control or regulating unit and transferred to the (not shown) control or regulating unit of the 6-axis industrial robot via a data line. The control of the actuators of the industrial robot and the monitoring of the actual position and comparison with the target position by the control system ultimately enables the path to be guided along the corresponding 3D object surface.

A calibration unit 4 is used to determine the TCP of a tool or a measuring device. If an LDV 2 or a two-beam LDV is used, such a calibration unit 4 can essentially consist of a CCD sensor of a commercially available digital camera. In order to avoid the destruction of the sensor pixels, the laser light can be weakened by filters before it hits the sensor.

The principle of calibration essentially consists in moving the industrial robot 1 with the LDV 2 until the area of the intersection of the two lasers l1, l2, ie the projection area of the intersection S or the measurement volume M onto the CCD sensor, is minimal where the bisector W of the intersecting laser beams is ideally orthogonal to the CCD sensor. Through the knowledge gained about the Position of the LDV relative to the calibration unit - the position of the calibration unit 3 relative to the coordinate origin is already known - the TCP can be determined. The calibration unit 4 can, as in Fig. 1 shown, be attached directly to the industrial robot, preferably to its base.

In another embodiment, a calibration unit 4 can also be positioned at any desired position within the working space of the parallel or serial kinematics. More preferably, the filter that attenuates the laser light is attached to said profile rail and the calibration unit 4 is attached in an area in the working space of the industrial robot.

In Fig. 2 two intersecting lasers l ₁ , l _{2 are} shown schematically. The point of intersection S forms the measurement volume in which an interference pattern in the form of interference fringes is formed. In the event that the two lasers l ₁ , l ₂ emit light of the same wavelength, the interference pattern is static, the interference fringes being oriented _{essentially parallel to the bisector W of the two intersecting lasers l 1} , l _2.

A particle p passing through the measurement volume with a resulting velocity v Scatters the light of the interference fringes periodically with the signal frequency f _S , which is proportional to the velocity component of the particle p orthogonal to the interference fringes (equation 4).

In the special case in which a particle p passes the interference fringes orthogonally, the magnitude of the resulting velocity becomes v , so | v | measured. If the measurement volume is positioned sequentially at different points P _i ' , the amount of the resulting speed can be | v _i | can be measured at the corresponding point. A vector field F can then be generated from all measurements. The vector field contains the information on the speed of a fluid flow in a region which is determined by the distribution of the points P _i ' .

A great advantage of measuring the magnitude of the resulting speed | v _i | of a particle p at a point P _i ' is that the corresponding velocity components v _{x i} and v _{y i} can be determined. This makes it possible to use a single measurement at a point P _i 'to determine two speed components v _{x i} and v _{y i} to investigate. With a multi-beam LDV, three velocity components v _{x i} , v _{y i} and v _{y i} can be determined, whereby the bisectors of, for example, two two-beam LDVs can be conceivable and the interference fringe patterns of the respective measurement volumes are ideally orthogonal to one another.

In Fig. 3 a wing is shown in section as an example of an object. The wing has an object surface O. Three points P ₁ , P ₂ , P ₃ on the object surface O are shown for illustration. The corresponding tangential planes T ₁ , T ₂ , T ₃ can be determined via the directional derivatives at points P ₁ , P ₂ , P _3. To determine a single tangent at points P ₁ , P ₂ , P ₃ , a directional derivative is sufficient.

From the geometry model of the object surface, for example that of the wing Fig. 3 , software known from the prior art (e.g. CAM software) can be used to create a flow chart in the form of programs (e.g. NC programs), which defines the trajectory along which a tool and / or a measuring tool is to be navigated . In addition to the trajectory to be followed, it is also possible to define which spatial orientation a tool and / or measuring device should have at a specific point P _i '. The orientation is defined via the tool coordinate system, the z-axis of this coordinate system corresponding to the tool axis which determines the orientation.

In the case of a speed measurement of a fluid flow in the vicinity of the object surface O, the point of intersection S or the measurement volume M of two intersecting laser beams l ₁ , l _{2 of} a two-beam LDV according to a flow chart (sequential) at points P ₁ ', P ₂ ', P ₃ 'positioned, the points P ₁ ', P ₂ ', P ₃ ' being located at corresponding distances a ₁ , a ₂ , a _{3 from} the object surface O and on the corresponding lines L ₁ , L ₂ , L ₃ , where the points P ₁ ', P ₂ ', P ₃ 'at a distance from the object surface and the points P ₁ , P ₂ , P ₃ lying on the object surface lie on the lines L ₁ , L ₂ , L ₃ , the bisector W of two laser beams l ₁ , l ₂ in each of the points P ₁ , P ₂ , P _{3 is} congruent with the corresponding lines L ₁ , L ₂ , L ₃ , the bisector W in each of the points P ₁ , P ₂ , P ₃ each is essentially orthogonal to the corresponding tangential plane T ₁ , T ₂ , T ₃ . It should be noted that only those points and lines with the same index belong together.

A trajectory B can be determined by interpolation between points P ₁ ', P ₂ ', P _{3 '.} The trajectory B is essentially parallel and runs at a certain distance from the object surface O. The trajectory B can, however, also run arbitrarily in the vicinity of the object surface O, ie the distance a _{i of} the points to be interpolated from the object surface can vary.

The object surface itself is described by the points P _i ( i = 1, ..., N ), the points P _{i being determined} either from an existing geometry model or by means of a device for contactless detection of 3D object surfaces as described above . A data processing device, for example a computer with known software or CAD software, assigns each point P _{i to} a coordinate system. In other words, the coordinates x _i , y _i , z _i of each point P _{i are} assigned to a coordinate system. Such a coordinate system is preferably Cartesian. Alternatively, the description of the points P _{i can be provided} in a polar coordinate or cylindrical coordinate system or a spherical coordinate system.

With the data obtained in this way, the points P _i 'can be set at a distance a _i from the points P _i lying on the object surface, the trajectory B corresponding to the interpolation function between the points P _i'.

If the object surface is located behind an optically transparent object housing, it may be that the measuring points P _i 'no longer have the desired position and orientation relative to the object surface. The object housing can be, for example, an angular or tubular wind tunnel made of optically transparent material. The optically transparent object housing causes optical refractions, including the laser beams of the LDV. In a preferred embodiment variant, the optical refraction of an existing object housing is therefore taken into account in the planning or while the measurement is being carried out. This allows the alignment of the LDV to be corrected accordingly.

The geometry or the optical properties of the object housing, the knowledge of which is necessary for the corresponding alignment of the LDVs, can either be known or be determined in advance with the aid of the LDVs and kinematics.

In one embodiment variant, a method according to the invention is used to record the movement of an object surface to be measured essentially in real time, as a result of which the trajectory can be adapted to the movement essentially in real time.

It has been shown that the necessity of only a single measurement at a specific point P _i 'enables an adaptive or dynamic adaptation of the trajectory B for object surfaces in motion (eg oscillating or rotating wing). This is for conventional measurement methods in which the speed components can be determined via two measurements at a point P _i '(with different orientations of the measurement volume), not possible or only possible to a limited extent, since the position of the corresponding point P _i ' changes relative to the coordinate system between the measurements. As a result, the measurement using conventional methods is flawed.

Claims (14)

Method for measuring the flow of fluids in the vicinity of an object surface (O) with a laser Doppler velocimeter (2) attached to parallel or serial kinematics with at least 6 degrees of freedom (1), the laser Doppler velocimeter at least one intersecting laser beam Forms pair (l ₁ , l ₂ ), the common point of intersection (S) of the at least one laser beam pair forming a measurement volume (M), the measurement volume (M) having at least one interference pattern with interference fringes, the interference fringes parallel to the bisector ( W) of the at least one laser beam pair are aligned, the measurement volume (M) being positioned one after the other at all points P _i ' ( i = 1, ..., N ), the speed of a fluid flow being measured at points P _i ', wherein the points P _i ' each lie at a certain distance ( a _i ) from the object surface (O) on lines L _i , the lines L _i each being orthogonal to the tangents Tial planes T _{i of} the points P _i located on the object surface (O) lie (with P _i ≠ P _{i + j} , j ∈ {1, ..., N }) and the points P _i each lie on the lines L _i , characterized in that the bisector (W) of the at least one laser beam pair (l ₁ , l ₂ ) is always positioned essentially orthogonally to the tangential planes T _{i of} the points P _i for i = 1, ..., N. Method according to Claim 1, characterized in that at each point P _i ' ( i = 1, ..., N ) the magnitude of the resulting speed v _i a fluid flow is measured, the resulting speed depending on the orientation of the measurement volume (M) through $\left|{\overrightarrow{v}}_i\right|=\sqrt{v_{x_i}^2+v_{y_i}^2}$

or $\left|{\overrightarrow{v}}_i\right|=\sqrt{v_{x_i}^2+v_{z_i}^2}$

or $\left|{\overrightarrow{v}}_i\right|=\sqrt{v_{y_i}^2+v_{z_i}^2}$

is given, where v _{x i} , v _{y i} and v _{z i} denote the velocity components of the fluid flow in three spatial directions (x, y, z ). Method according to Claim 1, characterized in that the coordinates x _i , y _i , z _i of all points P _i on the object surface (O) are determined by extraction from an existing geometry model. Method according to Claim 1, characterized in that the coordinates x _i , y _i , z _i of all points P _i on the object surface (O) are determined by a method for detecting 3D object surfaces. Method according to one of Claims 1 to 4, characterized in that the TCP (Tool Center Point) of the laser Doppler velocimeter is determined by means of a calibration unit (4) where the TCP of the laser Doppler velocimeter indicates the translational and rotational displacement relative to the center of the flange plate of a parallel or serial kinematics with at least 6 degrees of freedom (1). Device for following at least one trajectory (B) in the vicinity of an object surface (O), comprising parallel or serial kinematics with at least six degrees of freedom (1), in particular a six-axis industrial robot, and a device from the group of measuring devices or tools (2) with a tool coordinate system, characterized by at least one control or regulating device which contains geometry data of the object surface (O), the orientation of the device (2) along the at least one trajectory (B) being defined from the geometry data, the The tool axis is orthogonal to the tangential plane T _{i of} all points P _i ( i = 1, ..., N ) located on the object surface (O), the at least one control or regulation device being the parallel or serial kinematics with at least six degrees of freedom ( 1) controls. Device according to Claim 6, characterized in that the control or regulating device receives data from a device for contactless detection of 3D object surfaces (3), a geometry model being generated from the data obtained. Device according to claim 6 or claim 7, characterized in that the control or regulating device has a post processor, the post processor translating the instructions for the parallel or serial kinematics with at least six degrees of freedom (1), the control or regulating device the actuators of the controls and / or regulates parallel or serial kinematics and specifies and / or monitors the movement along the at least one trajectory (B). Device according to one of Claims 6 to 8, characterized in that the device from the group of measuring devices or tools (2) is a laser Doppler velocimeter. Device according to Claim 9, characterized by a calibration unit (4) for the laser Doppler velocimeter (2), the calibration unit (4) having a CCD sensor. Device according to one of Claims 6 to 8, characterized in that the device from the group of measuring devices or tools (2) is a laser cutting device, a welding device, a glue gun, a paint gun. Device according to Claim 7 and one of Claims 8 to 11, characterized in that the device for capturing a 3D object surface (3) has either a 3D scanning unit, preferably a 3D laser scanning unit, or a camera, preferably at least one digital camera. Method for determining a trajectory (B) in the vicinity of an object surface (O) with a device according to one of claims 6 to 12, wherein the object surface (O) is detected with a device for non-contact detection of a 3D object surface (3), whereby a three-dimensional point cloud corresponding to the object surface (O) is obtained, characterized in that the control or regulating device assigns all points P _{i of} the three-dimensional point cloud of the object surface (O) to a coordinate system and each point P _i coordinates x _i , y _i , z _i are assigned, the coordinates x _i ', y _i ', z _i 'of points P _i ' at a distance ( a _i ) from the object surface (O) being determined from the coordinates x _i , y _i , z _{i, with} is interpolated between points P _i '. Method according to Claim 13, characterized in that the device for detecting a 3D object surface (3) is used to detect a movement of the object surface (O) essentially in real time.

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